At the conclusion of our webinar, Defining Stack-Ups for Flex and Rigid-Flex Circuit Boards, we had several questions submitted to our presenter, Zachary Walker, Product Manager of Flex and Rigid-Flex Circuits at Epec. We have compiled these questions into a readable format on our blog.
Q&A From Our Live Flexible PCB Webinar
Quick Links:
- Can Epec supply a custom stack-up for my build?
- Do your stack-ups consider impedance?
- Is there any way to increase the flexibility of a flex without decreasing the layer count?
- What is the cutoff for static and dynamic bends?
- Can signal isolation strategies such as picket fences and via stitching still be utilized on a flex PCB?
- Can you please explain how airgap requirement is maintained during fabrication?
- Does my design need to be finished prior to sending you the mechanical and layer stack?
- For a rigid-flex, are blind and buried vias allowed for both the rigid and flex portions of the design, or is it one or the other?
- Must transition zones be identified in Gerber files, or do manufacturers automatically add these zones?
Watch the Recording Below:
Question: Can Epec supply a custom stack-up for my build?
Answer: Epec can supply custom stack-ups if you contact us and present your design to us. Typically, we like to review it over a call, but if we were to review a design together, we can recommend a stack-up. Or, if push comes to shove, if you were to submit a thickness copper weight requirement use case to us, we can usually get back a custom stack-up. And, if need be, for reference, we can also submit our standard stack-ups that we can then base custom stack-ups off of and work together to suit your needs.
Question: Do your stack-ups consider impedance?
Answer: Our standard stack-ups that were shown in this webinar, alongside our typical stack-ups that we will send to customers, do not consider impedance. However, that is not to say we could not consider impedance. We have many stack-ups and impedance configurations in our hands, and we have the programs to be able to calculate it out as well. So, if you were to come to us with a necessity for impedance 50Ω, single-ended 100Ω differential, or anything of that nature, we would be able to support it and we'd be able to do a stack up for you with that impedance in mind.
Question: Is there any way to increase the flexibility of a flex without decreasing the layer count?
Answer: The best way to increase flexibility beyond decreasing layer count will tend toward copper weight being a primary driving factor. If greater flexibility is needed, we'll go from 1 ounce to 1/2 ounce or 1/2 to 1/3 ounce. After that, it's dielectric thicknesses. So, with heavier copper weights like 1 or even 2 ounces, that will require thicker amounts to cover the adhesive, whereas decreasing it will decrease the dielectric of both the inner core and the cover adhesive. Generally, the best way to increase flexibility is copper weights followed by a dielectric, and then you can buy a little bit of flexibility. If you were to have planes and you were to convert your plane layers to cross-hatch planes, however, the degree of flexibility you're buying back by doing cross-hatch would not be anywhere comparable to decreasing the copper way or by decreasing the core corps or cavalry.
Question: What is the cutoff for static and dynamic bends?
Answer: IPC-2223 will typically define static bends as bends, more so towards the single-digit count. They'll use terms like flex to install or things of that nature. Because static bends are meant to, you bend it once, twice, maybe 4 or 5 times in total. For example, if you have to do maintenance on a design or things of that nature, and you're not really intending to bend it more than 10 times at most. But IPC-2223 just kind of exemplifies static and dynamic bends. It doesn't really do a cut-off, so we would have to have a discussion and review the design, especially since there's such a difference between static bins being a single amount of bends versus dynamic bends being per IPC functionally infinite number of bends.
Question: Can signal isolation strategies such as picket fences and via stitching still be utilized on a flex PCB?
Answer: Signal isolation strategies are quite common in both flex and rigid-flex PCBs. We have a long history of supporting customers who have implemented both picket fences and via stitching in their designs without any issues.
Question: Can you please explain how airgap requirement is maintained during fabrication?
Answer: Airgap is done by constructing the flex sections individually, and then laminating it together during the final lamination with the rigid section. Once constructed, the gap is kept by the separation of the two layers due to the location of both within the rigid construction.
Question: Does my design need to be finished prior to sending you the mechanical and layer stack?
Answer: The design does not need to be finished for a budgetary quote. However, the design would need to be finished and reviewed before we could proceed to production if it matches with the specifications outlined during the budgetary quote.
Question: For a rigid-flex, are blind and buried vias allowed for both the rigid and flex portions of the design, or is it one or the other?
Answer: Blind/buried vias are not required to be in one or the other section and can in fact cross from rigid to flex sections, or vice versa. In some instances, depending on if aspect ratios allow it, they can even cross from the rigid section down through the flex layer and to a rigid layer on the other side.
Question: Must transition zones be identified in Gerber files, or do manufacturers automatically add these zones?
Answer: Transition zones do not need to be defined by customers. We would prefer all rigid areas to be outlined within Gerber files or drawings, and from that, we measure the spacing from via to the rigid outline to determine that transition zone spacing for vias.
Watch Our Video:
Designing Flex and Rigid Flex PCB Stack-Ups with Advanced Software
See our in-depth tutorial on creating a stack-up using our advanced software! In this video, we walk you through the process of generating a new stack-up, starting with the default settings and customizing it to fit your specific requirements.
